The present invention relates generally to electrically controlled key actuated locks.
In an effort to provide for greater security in door locks, security devices and alarm systems, there has been developed heretofore a multiplicity of control circuits for controlling the actuation of an electric bolt or signal alarm by means of a key member which is utilized to insert one or more circuit components into the control circuitry. These prior art arrangements have ranged from simple to complex, and relatively vary with respect to their security effectiveness.
For example, it is broadly known from U.S. Pat. Nos. 3,921,040 and 3,518,655 to utilize in an electronic lock a balanced bridge concept and an insertable key containing a resistor which forms one leg of the bridge. U.S. Pat. No. 3,673,467 discloses an arrangement which utilizes two bridge circuits with a key arranged to insert resistance components in each bridge circuit.
U.S. Pat. Nos. 3,347,072 and 3,134,254 disclose the broad general concept of utilizing a control key with a circuit element therein, an oscillator, an output circuit containing an amplifier and a solenoid coil to retract a bolt.
It has also been known generally from U.S. Pat. No. 4,013,930 to utilize in an electric door lock, two timing circuits to actuate the door-opening mechanism. The second timer fires a Schmitt type trigger.
Another approach is disclosed in U.S. Pat. No. 3,656,001 which utilizes a single bridge arrangement with two of the bridge components being contained in the key. The arrangement includes a relay having contacts which can be utilized for the control of a solenoid operated door lock, this relay being controlled by obtaining zero output simultaneously from two or more balanced circuits and a controlling key device.
While the present invention utilizes a key for inserting components into the bridge network and an oscillator network for the control of a control relay for the electric lock device, the elements are in general associated in a differently combined arrangement which utilizes the output of the bridge network to operate regenerative differential electronic switches that are connected to selectively activate a pair of relays with series connected contacts in accordance with the direction of unbalance of the bridge, and to activate both relays in response to a balanced operative mode of the bridge so that the relay contacts will coact to close a voltage connection to the oscillator network. The arrangement is entirely different from that disclosed or taught by any of the noted prior art patents.